An electric power steering system refers to a device for changing the direction of wheels through a steering wheel, in order to change the direction of a moving car. A recent electric power steering system includes a steering angle sensing device and a torque sensing device to provide driving stability and users' convenience.
The steering angle sensing device refers to a device for sensing a steering degree to control a moving car, and the torque sensing device refers to a device for sensing torque applied to a torsion bar to provide an auxiliary control power such that a steering wheel may be smoothly controlled.
The steering angle sensing device and the torque sensing device may be separately provided and mounted in the electric power steering system. Alternatively, the steering angle sensing device and the torque sensing device may be provided as a single device and mounted in the electric power steering system.
The steering angle sensing device and the torque sensing device are assembled together with other components such as a housing and then mounted in the electric power steering system. Hereinafter, the steering angle sensing device and the torque sensing device are referred to as a sensing device, and the steering angle sensing device and an assembly of other components, the torque sensing device and an assembly of other components, and the steering angle sensing device, the torque sensing device, and an assembly of other components, respectively, are referred to as “power steering sensor assembly”, for convenience of description.
Since the sensing device is sensitive to the external environment, the sensing device is mounted in a sealed housing. That is, the power steering sensor assembly includes the above-described sensing device and first and second housings for housing the sensing device.
The sensing device positioned in the housing should be fixed inside the housing. For this structure, an auxiliary member such as an O-ring is mounted on the outer circumferential surface of the sensing device, and the sensing device is then positioned in the housing.
In such a state, the outer circumferential surface of the O-ring is closely attached to the inner circumferential surface of the housing. Accordingly, the sensing device is fixed and mounted in the housing.
However, the above-described structure including the sensing device mounted in the housing has a problem in that an additional member such as the O-ring should be prepared and coupled to the sensing device.
Furthermore, in an electric power steering system mounted in a vehicle to which an outer force (impact) is repetitively applied, an O-ring may be distorted from the original position or may come off from the sensing device.